I have a 2014 with the tow package, I want to charge my batteries in my trailer when i tow it. my trailer had a 4pin that i changed to a 7 and added the power wire to the trailer batteries and also grounded them, the dealer said that it was factory setup so the power wire would not let the trailer batteries pull power from the main battery, but after connecting everything up i noticed that the power wire is always hot, does any know if ther is some kind of built in isolator or silenode installed. I bought one that i was going to install but they said i didnt need it.

The way it should work is power goes out to the trailer on the 7 pin plug. This is typically used to run interior trailer lights. As far as charging a battery in the trailer you might get somewhat of a trickle charge but chances are the wiring is just too small. If you really want to charge the battery from the truck I suggest running a new heavier gauge wire and installing an ACR in the trailer or on the truck.

The relay silenode that i ordered does the same thing, just rated at higher amp's. The next quesiton is can i just replace the constaint 12v wire in the 7pin with the new larger gage and will 10 gage be good or should i go wih 8

Problem I see is the wire running in the truck is going to be small running from your fuse block, upgrading the wiring at the hitch probably won't do much. I suggest you run a new wire from the battery/fuse block to your trailer on some sort of quick disconnect with the relay in line. Depending on the run and how low you typically deplete the trailer battery I'd say 8ga should be fine, only has to charge the battery not run your accessories.

That was the plan, Run a new 8 gage from the truck battery to the 7pin with a inline 30amp fuse also should i add a larger ground wire. The run will be about 6ft from the back of the jeep. and the trailer batteris a dual marine deep cells running light and power poles insde that trailer for chargeing RC plane batteries so only chargeing enroute to the field should be good

I think your going to lose the benefit of the 8ga if you run it through the 7 pin, pretty small terminals in there.

How long of a drive with the trailer? Will it have time to charge the batteries? I use a deep cycle group 31 on my boat lift and keep it topped up with a solar charger, occasionally it needs to be plugged in. Have you considered that? Might be easier than running wires through the truck since the truck will only charge the trailer batteries when it's running.

The normal drive is around 30 or 40 minutes, but I do several long trips during the summer and i do put a good drain on the batteriesseveral take about 6000mah per charge and then i have sat radioand speakers but i do leave the solar pluged in , i did try just the solar panles last year and they couldnt keep up on long weekends. Ill look and see if i can find a large gage quick connect that i can mount near the 7 pin for power i just want the install to look clean.

If your draining batteries that much you may want to consider a thicker wire. 8ga is kinda small but would be easier to work with. Maybe consider 6ga or 4ga, you not only have the wiring in the truck but the wiring in the trailer too. So ~6ft run in the truck and another 4-5ft to the trailer, that's getting pretty long for 8ga even 6ga wire IMO. The amps may drop enough that it wont even charge the batteries with a smaller gauge wire. And ya I highly recommend a new ground in whatever size wire you end up going with to the truck. Then something like this for your quick disconnect. Quick Disconnect

Well, pin 4 of the standard 7 way RV connector is identified as "12 volt charging". However none of the vehicles I have owned had any kind of isolater that would prevent running down the vehicle battery if left plugged in long enough while drawing current. It is definitely hot all of the time.

I know that pin 4 stays hot on my pickup and I even use it to power a small portable winch to pull cars up on my flat bed trailer.

If you don't deplete the batteries too much the factory wiring or the 8ga i originally suggested should be fine. But if your depleting the batteries quite a bit and want them to charge up faster go with the heavier wire.